The present invention relates to an organic electroluminescent display device including light-emitting films containing organic electroluminescent materials.
The present application claims priority from Japanese Patent Application Nos. 2002-209869 and 2002-281110, the respective disclosures of which are incorporated herein by reference.
It is known that the electroluminescence (hereafter, referred to as EL) of organic compound materials which emit light by current injection is utilized in display devices (organic EL display devices) The EL display device has many pixels arrayed in a predetermined pattern on a planar substrate. Each pixel is composed of organic EL display elements made of organic EL films.
As a result of research efforts, organic compound materials which can emit red (R), green (G) and blue (B) light of high purity have been developed, which are suited for organic luminescent displays represented by the organic EL display device. Now full color display devices are available which have R, G and B light-emitting elements in each pixel.
FIG. 1 is a diagram illustrating a prior art organic electroluminescent display device, which is capable of providing color images, as disclosed in Japanese Patent Application Laid-open No. Hei 8-227276. On a transparent substrate 1, this organic electroluminescent display device has scan signal lines 2 and data signal lines 3 which are arrayed to intersect at right angles and electrically isolated from each other, non-linear elements 4 each connected to the scan signal line 2 and the data signal line 3, and first display electrodes 5, which are connected to the non-linear elements 4, of independent array patterns each corresponding to the R, G and B light-emitting elements. On the first display electrode 5, a different organic electroluminescent film is deposited for each color, and a common second display electrode (not shown) is further deposited on the organic electroluminescent film.
In such an organic electroluminescent display device, R, G and B light-emitting elements constitute a display unit (pixel) in combination, and full-color images are provided by driving the individual light-emitting elements.
In addition, Japanese Patent Application Laid-open No. Hei.11-52905 discloses a technique using two light-emitting diodes (LEDs) of different colors per pixel for providing multicolor images by mixing the two gray-scaled colors.
There is a problem in the former case, i.e., in the conventional organic electroluminescent display device where a display unit is composed of three light-emitting elements, that the ratio of luminescent areas per pixel (aperture ratio) is low. This is because non-luminescent margins for wiring exist around the light-emitting elements. Another problem posed in the prior art is that the manufacturing process is complex because the three light-emitting elements need to be formed one by one on the substrate.
The above problems could be avoided by constituting the light-emitting elements with a single light-emitting element per pixel. However, in turn, there arises another problem that such a display device only provides monochrome gray-scale images, instead of versatile color images.
Moreover, in using LEDs as light sources as shown in the latter prior art, it is difficult to precisely control the chromaticity of emitted light. Therefore, high-quality two-color images are not provided by such an approach because of the limited chromaticity range attained by mixing LED colors.